Lead holder drafting compass

ABSTRACT

A frame held drafting compass for drawing circles wherein the compass pivot is located at the center of the circle to be drawn and the base of the frame contacts the drawing surface outside of the circle to be drawn, so that a contact point at the center of the circle to be drawn is unnecessary. The scribing structure includes a lead holder adjustable so that the angle of incidence of the lead to the paper can be varied.

United States Patent 7 Killgrove [151 3,656,237 [451 Apr. 18, 1972 [54]LEAD HOLDER DRAFTING COMPASS [72] Inventor: Thomas 0. Killgrove, P.O.Box 395, Frazi er Park, Calif. 93225 [22] Filed: Nov. 18, 1970 21 Appl.No.: 90,757

[52] US. Cl. ..33/27 D [51] Int. Cl .....B43l 9/02 [58] Field of Search..33/27 [56] References Cited UNITED STATES PATENTS 1,402,961 1/1922Ratcliff ..33/27 D FOREIGN PATENTS OR APPLICATIONS 675,033 10/1929France ..33/27D 1,030,194 6/1953 France ..33/27D PrimaryExaminer-William D. Martin, Jr. Assistant Examiner-Charles E. Phillips57 ABSTRACT A frame held drafting compass for drawing circles whereinthe compass pivot is located at the center of the circle to be drawn andthe base of the frame contacts the drawing surface outside of the circleto be drawn, so that a contact point at the center of the circle to bedrawn is unnecessary. The scribing structure includes a lead holderadjustable so that the angle of incidence of the lead to the paper canbe varied.

5 Claims, 8 Drawing Figures strument of the character described abovehaving a quick and easily changed adjustment for setting the length ofradius of the circle to be drawn.

A still further object of this invention is to provide a device of theabove type. for drawing circles that does not require punching a hole inthe drawing surface at the center of the circle to be drawn.

Another object of this invention is to provide a device of the abovetype which will guide a lead holder lead point about a circular pathwhile at the same time pennitting angular motion of the guided leadholder about the lead point.

Yet another object of the invention is to provide a device of the abovetype having a pivot at the center of the circle being drafted which iseasily positioned by a supporting structure whose base rests at alocation outside of the circle, such that a supporting point or restingsurface at the pivot is unnecessary.

Other objects and advantages will become apparent from the followingdetailed specification and accompanying drawings, in which:

FIG. 1 is a perspective view of this invention;

a FIG. 2 is a plan view of the rotatable portion of the compass, takenon the line 2-2 of FIG. 1, looking in the direction of the arrows;

FIG. 3 is a fragmentary sectional view of the handle and base structure,taken on the line 3-3 of FIG. 1, looking in the direction of the arrows;

FIG. 4 is an enlarged fragmentary sectional view of the pivot, taken onthe line 4-4 of FIG. 2, looking in the direction of the arrows;

. FIG. 5 is an enlarged fragmentary sectional view of the locking camand rotating housing, taken on the line 5-5 of FIG 2, looking in thedirection of the arrows;

FIG. 6 is a fragmentary sectional plan view of the locking cam androtating housing, taken along line 6-6 of FIG. 5,

looking in the direction of the arrows;

FIG. 7 is an enlarged fragmentary sectional view of the lead holderguide, taken along line 7-7 of FIG. 2, looking in the direction of thearrows; and

FIG. 8 is a fragmentary sectional view of the pivot support structureboom, taken along line 8-8 of FIG. 1, looking in the direction of thearrows, and also showing the position of the lead holder guide, inbroken outline, when that portion of the compass is rotated from theposition shown in FIG. 1 to a position adjacent to the supportingstructure boom.

Referring now to the drawings in detail wherein like reference numeralsindicate like parts throughout the several figures, the referencecharacter 9 generally designates one embodiment of the lead holdercompass constructed in accordance with this invention.

The lead holder compass 9 includes a flat base plate 10 which is aboveand parallel to the drawing surface, not shown in this view, and isrigidly connected to a vertical plate member 11 which is in turn rigidlyconnected to the T-shaped boom portion 12 which is again in turn rigidlyconnected to the cylindrically shaped boom extension 13. This group ofelements referenced as 10, ll, 12, and 13 are shown as being constructedfrom a single metal casting of a suitable material such as aluminum.

FIG. 3*shows in cross sectional view the upper portion 14 of theT-shaped section which extends across the curved top of plate 11 andwhich,as seen in FIG. 1, passes the plate 11 and continues on to formthe upper part of boom 12. A thin sheet 15 is bonded or molded to thebottom surface of plate 10. Sheet 15 provides thesurface for base 10which rests upon the drawing surface. The sheet material is a neoprenerubber or a similarly suitable rubberlike or plastic material which hasa high coefficient of friction in combination with paper or draftingvellum.

Referring now to FIGS. 1, 2, and 4, the rotating housing 16 contains andjoins other parts of the roatable portion of the compass. Two lowerdisc-like segments 17 of housing 16 extend on either side of the thickerportion 18, and are parallel to the drawing surface. A discontinuationbetween segments 17, at the side opposite guide base 19, produces a voidregion between edges 20. The thicker portion 18 is of a rectangularplate shape containing holes required to join or contain parts of therotatable assembly, being parallel to the plane of the drawing surface,and with the lower surface 21 being common with lower surface of plateportions 17. Housing 16 is constructed from Lucite plastic or for asimilarly suitable transparent material. Stud 22 connects housing 16 tothe boom extension 13 by threads 23. Housing 16 is suspended by studhead shoulder 24 in a position such that the lower surface 21 isslightly above the drawing surface. A close running fit exists betweenstud 22 and the mating hole in housing 16.

In FIG. 1 the positioning rods 25 are shown suspended in the housing 16by being passed through loose fitting holes 26. When viewed in FIG. 2,rods 25 with holes 26 are equally disposed about a centerline passingthrough the center of stud 22. Rods 25 are constructed by forming asmall round rod of stainless steel or other suitable metal into a narrowU-shaped piece with parallel legs.

Referring now to FIG. 5, cam lock 27 fits into a round flat bottomedclearance hole midway between and partially intersecting the rod holes26. With the interlocking of bottom edge 28 underneath rods 25, cam lock27 is prevented from withdrawl by interference. The finger tab portion29 projects vertically above the top surface of housing 16. Cam locksurface 30 is depicted as being rotated to the unlocked position, therebeing a clearance around rods 25. In FIG. 6, the profile of cam surface30 shows that upon rotation of the cam lock within its socket by therods 25 will be caused to spread aparttowards hole surfaces 31 withinhousing 16. Cam lock 27 is constructed from nylon plastic, or from asimilarly suitable plastic material.

As viewed in FIGS. 1, 2, and 7, the guide base 19 is composed of anattaching pad 32, two stabilizing pads 33, and a disc-like hemisphericalportion 34, all being a common piece of material suitably connected bycontouring and blending of 32, 33, and 34 together. The attaching pad 32is firmly attached with a suitable bonding material to the ends of rods25 which are installed into holes 35. The vertical centerline of hole 36in hemispherical portion 34 passes through the theoreticalcenter pointof 34. The two pads 33 which rest upon the drawing surface are formed asrounded bumps and are the only surfaces of guide base 19 which contactthe drawing surface. As constructed and thus positioned, the theoreticalcenter point of hemispherical portion 34 lies on the drawing surface,midway between stabilizing pads 33, and when viewed in FIG. 2, it alsolies on a theoretical centerline parallel to and midway between rods 25.Guide base 19 is constructed from a suitably clear plastic material suchas Lucite.

, In FIG. 1, the reference 37 is a gauge mark visibly impressed acrossboth sides of part of the upper surface of housing 16. A

similar gauge mark 38, parallel to mark 37, is shown upon the topsurface of guide base 19. Gauge marks 37 and 38 are also viewed in FIG.2, which shows them as seen in the plan view to be perpendicular to thelong axis of rods 25, with mark 37 being coincidental with a centerlineof stud 22, and with mark 38 being coincidental with a centerline oflead holder hemispherical portion 34.

Pivot alignment marks 39, 40, 41, and 42 are visibly impressed onto thelower surface 21 of housing 16, these marks being at 90 and 45 withrespect to each other, and with all of them being in coincidence with atransverse centerline of pivot 22, as viewed in the plan view FIG. 2.The lines 43 and 44 are visibly impressed onto the lower surface ofguide base 19. As viewed, these lines are coincidental with centerlinesof spherical portion 34, and at right angles to each other. Line 44 isperpendicular to the long axis of rods 25, and line 43 appears as anextension of line 39 of housing 16.

FIG. 7 shows the round tubular shaped lead holder guide 45 with thelower end contoured to match, in a coaxial fashion, the hemisphericalportion 34, and with an internally threaded portion 46 at the lower endof the inside diameter. Lead holder guide 45 is constructed from Luciteplastic or from another suitable transparent material. The inner surface47 provides a loose fitting socket receptacle for the lower portion ofthe lead holder, not shown. The lead holder guide retainer 48 is alsoconstructed from Lucite plastic or other suitable transparent material,and it consists of an externally threaded portion 49, a small round hold50, which provides a clearance fit for the drawing lead, not shown, atapered entry 51, and a head 52 which iscontoured to match lower surfaceof hemispherical portion 34, and which also provides an extension ofthis lower surface, as indicated at reference 53, and thereby alsoprovides an annular clearance around hole 36. Male thread 49 is showninstalled into female thread 46, this being possible by having thecentral hole 36 the same diameter or slightly larger than theinterfering diameter of thread 49. The spherically contoured and shapedsurfaces around hemispherical portion 34 are loosened or tightened bythe threads to provide a close sliding fit. After obtaining the correctfit, a plastic or metal set screw 54 is installed into the lower body ofguide 45, the end of the set screw 54 pressing against the male threads49. All hemispherical surfaces are constructed to have a common centerpoint. The lead holder guiding surface 47 and the lead hole 50 have acommon axial centerline which, if extended downward, passes through thecommon hemispherical center point.

In FIG. 8 a cross sectional view of the boom 12 shows an upper point 55and a lower point 56. These are contacting points on the right hand sideof boom 12 for the outer diametral surface of guide body 45, when thelead holder guide is rotated to the position shown by the broken lines.Corresponding points on the left hand side of the boom 12 become thecontact points when the lead holder guide is rotated around to thatside.

Having thus described in detail the construction and the various partsof the lead holder compass, I will now describe how, by using thiscompass together with a drafting lead holder with lead, not shown in thedrawings, a full circle or an arc may be drawn.

Centerlines of the circle to be drawn are first laid out in the usualmanner, crossing the desired center point on the drawing surface and atright angles to each other. Next, the radius is established. This may beaccomplished in one of three ways. The first method uses the gauge marks37 and 38 together with a suitable drafting scale, ruler or dividers,not shown in the drawings. Cam lock 27 is rotated within its socket bytwisting finger tab 29 until the cam is in the position shown by FIGS.and 6. Rods 25 are now free to slide within the housing 16, and guidebase 19 can now be freely positioned with respect to the pivot 22. Whenthe desired radius is obtained, as indicated by measuring the distancebetween gauge marks with the scale or dividers, the cam lock finger tab29 is twisted with the fingers by 90. Surface 30 now contacts rods 25,spreading them apart. Dimensions of the cam surface, the rods, and theclearance holes 26 are such that when the cam is in this position theouter surfaces of the rods touch the surfaces 31 of the housing.Friction between contacting surfaces on both sides of each rodeffectively bind the rods in a locked position.

The second method of establishing the radius is the same as the firstmethod, with the exception of using the gauge marks. Instead of directmeasurement of gauge marks 37 and 38, the lines 41. and are used byaligning them with previously drawn parallel lines on the drawingsurface. Visual alignment of the two previously drawn parallel linesspaced at the desired radius, with lines 41 and 44, will result in thedesired radius when locked in position by. the cam lock.

The third method of establishing the radius is the same as the secondmethod, with the exception that line 44 is not used. Instead, the leadhole 50 is used to sight a point on the drawing surface. With the leadholder removed, and the guide body held in a generally verticalposition, sighting of a point or a line on the drawing surface willresult in a correct positioning of the lead holder guide with respect tothe pivot, when used in conjunction with line 41, as with the previousmethod. It is also possible to establish the radius in a similar fashionbut with the lead holder installed, by sighting the lead point on thedrawing surface, through 34.

The next step in drawing a circle is to center the pivot over the centerof the circle. This is accomplished by visual alignment of either pairof lines 39 and 41 or pair 40 and 42 with the pro-drawn circleCenterlines. Either alternately or simultaneously, the roatable portionof the compass is turned to align the lines, while the compass is liftedor slid across the drawing surface to move it into position. A lightdownward pressure in the vicinity of the handle or base is sufficient tomaintain position of the compass while drawing the circle, however, thefriction of 15 against the drawing surface is not so great as tointerfere with deliberate, slow sliding of the compass into position.After the pivot is aligned, the lead holder guide is rotated to thevicinity of the boom 12. The lead holder with lead, not shown in thedrawings, is then installed with the lead fitting into hole 50 and thepoint touching the drawing surface. Using the lead holder body tomanipulate the guide and rotatable portion of the compass, the guidebody 45 is caused to touch the boom at the two points as shown by FIG.8. Since the guide surface now touches two seperated points, there is astabilizing effect. Also, when in this position, the lead point is at apoint on the drawing surface which is directly underneath or slightlypast a theoretical vertical centerline which bisects the boom crosssection shown in FIG. 8. Now, with the normally used downward forceapplied to the lead holder, the circle is drawn by rotating the guidearound with the lead holder. A natural motion, with no special regardfor vertical positioning of the lead holder is possible, since sphericalguiding of the lead point causes the lead point to follow a truecircular path. Also, the pads 33 help to maintain vertical position ofthe spherical guide with respect to the drawing surface, as well as toprevent torsional motion of the spherical guide about a theoreticalcenterline parallel to and between the rods 25. When the lead holderguide is rotated around to the opposite side of the boom, points on theboom are again contacted. The position of the guide body 45 can beobserved and felt by the stabilizing effect when contacting the twopoints on boom 12. Again, the lead point is at a point on the drawingsurface directly under or slightly past the theoretical verticalcenterline bisecting the boom cross section. Under the boom, the ends ofthe circle are joined, and the circle is completed.

It is obvious now, that a partial circle, or are, may also be drawn bythis compass. Procedures for drawing an are are the same as for drawinga full circle, however, when the boom 12 is positioned over the drawingsurface in such a location as to avoid the vicinity of the are beingdrawn, observance of the position of guide body 45 with respect to boom12 is not necessary. To limit the arc to some specific angularexcursion, any of the lines 39, 40, 41, or 42 may be used by employingvisual alignment with either angular boundaries or with a radial linepreviously placed on the drawing surface. For example, if the arc isdrawn beginning when line 41 is in coincidence with a radial centerlineon the drawing surface, rotation of the housing 16 in drawing the arcuntil line 42 is in coincidence with the same radial line will cause anarc of 45 to be obtained. Line 43 may also be used to advantage, bybringing it into coincidence with the desired angular boundaries on thedrawing surface, at the beginning and termination of the are beingdrawn. Also, the lead point itself may be viewed through the clearplastic guide elements, in order to establish location of the leadpoint. This is best accomplished by pivoting the guide body 45 away fromthe viewer, allowing the point to be sighted through hemisphericalportion 34 only, rather than through elements 34, 45 and 48 incombination.

Another useful aspect of this compass is the capability of drawing anare when the center lies off of the drawing surface, or when, for otherreasons, contact with a surface at the center of the arc is either notpossible or not desireable. The procedure for drawing such an arc is thesame as for drawing any are, excepting that locating of the compasspivot is accomplished by using line 43 in conjunction with a line on thedrawing surface. Several means are available for positioning the pivot.With the pivot off of the drawing surface, the base and the rotatableportion of the compass are moved until coincidence with line 43 and apre-drawn line is obtained. This pre-drawn line must be a projectionfrom the theoretical center point of the desired are. For the drawing ofan arc whose center lies off of the drawing surface, it is generallynecessary to have first established the desired radial distance by oneof the previously described methods. Alignment of the pivot may also befacilitated by having on the drawing surface a second line which is atright angles to the projected radial line and which crosses the radialline at the desired point of tangency. Again, line 43 is brought intocoincidence with the radial line, but line 44 is also brought intocoincidence with the second line. Another possibility for pivotalignment and placement is to place on the radially projected line, amark at the desired point of tangency. Either the lead hole 50 or thelead point is then used for locating the lead to this mark, and afterthe line 43 is brought into coincidence with the radial line, the arc isstruck with the lead holder and lead in the usual manner. Where greataccuracy is not required, the rods 25 may be used for alignment, since aradial line will lie between these when viewed in the plan view.Placement of the compass such that rods 25 are equal distance andparallel to a radial line on the drawing surface, will result in radialpositioning of the pivot which is sufficiently accurate for the largerarcs.

At this time it should be obvious that the guide 45 may be disengagedfrom retainer 48 after loosening set screw 54, and these parts may beeasily removed. The hole 36 is then readily accessible and provides amounting locator for other accesso- 40 ries, such as inking penadapters, scribing tools, or cutters. The disassembly of the rotatableportion of the compass by removal of screw 22 is also obvious. Thecompass is easily assembled from or disassembled into the seperate itemsof: base and frame, shoulder screw, rotating housing and guide base,lead holder guide, and lead holder guide retainer. The ease of assemblyand disassembly into the various parts facilitates packaging fortransportation and also makes the replacement of parts a simpleoperation.

From the previous descriptions it will be apparent that this inventionprovides a novel compass which is simple and rugged in construction,which may be economically manufactured, and which has a long servicelife.

Having thus described the preferred embodiment of the invention, itshould be understood that numerous structural modifications andadaptations and changes in the combination and arrangement of parts orelements as heretofore set forth in the specification and shown in thedrawings may be made without departing from the scope of the inventionas defined in the following claims.

What is claimed is:

l. A lead holder drafting compass comprising:

a flat base with a bottom friction surface, said base also including anupright handle member having an extending boom projecting over a drawingsurface, the end of said boom containing in the vertical axis a screwattachment hole;

a transparent rotating housing member, said housing having a verticalaxis bearing hole with a counterbore on the bottom side through which ashoulder screw is inserted and installed into said vertical axis screwattachment hole, said housing being held suspended above the drawingsurface upon which said base rests by the head of said shoulder screw,said housing having two parallel horizontal clearance holes equaldistanced from said vertical axis bearing hole, said housing also havinga flat bottomed vertical hole lying between and partially intersectingat the diameter of said flat bottomed hole said parallel horizontalclearance holes;

two rod members, longer than said housing, said rods being parallel toeach other and held within and passing through said horizontal clearanceholes in said housing, said rods being joined together at one end in onedirection from said housing, and with the ends of said rods protrudingfrom said housing in the opposite direction being attached to a leadholder guide base;

a cam lock member having a short vertical portion with a recessed camsurface in and around said cylindrical portion, and having a finger tabportion extending vertically upward, and with said short cylindricalportion installed into said flat bottomed vertical hole in said housing,and having said recessed cam surface contoured to cause alternatelyeither looseness or a tightening of said rod members between said camsurface and outer surfaces of said horizontal clearance holes when saidcam is rotated by said finger tab in a horizontal plane, and also havinga portion of said short vertical cylindrical portion lying below saidrod members and captured between said rod members and bottom of saidflat bottomed hole;

a transparent lead holder guide base member having a hemisphericallyshaped guiding disc portion concaved upward with a round hole in thecenter and with a hemispherical center point positioned at the drawingsurface, said hemispherically shaped disc being spaced off of thedrawing surface by two attached guiding pads equally spaced on oppositesides of said hemispherically shaped disc which contact the drawingsurface, and also positioned vertically by the joining of an attachedpad to the end of said rods which extend out of said rotating housingmember;

a transparent lead holder guide member of hollow cylindrical shapehaving an upper guiding bore of diameter slightly larger than a leadholder barrel, with the lower end of said lead holder guide having asurface contacting the upper surface of said hemispherically shaped discand being concentric with and normal to said guiding bore, the innerlower end of said lead holder guide having an internal thread concentricwith said bore, there also being a small set screw hole with a set screwpassing through the wall of said lead holder guide in the threaded lowerportion of said guide;

a transparent lead holder guide retaining member, having externalthreads matching said internal threads of said lead holder guide butalso with an interfering diameter the same as or smaller than saidcenter hole of said hemispherically shaped disc, and having a lead holeof slightly larger diameter than a drafting lead, said lead hole alsohaving a tapered entry at the upper end, with said lead hole beingconcentric with said external threads, with said guide retainer alsohaving a head at the lower end and being of larger diameter than saidcenter hole of said hemispherically shaped disc, said head beingcontoured to mate with the concave surface of the hemispherically shapeddisc and also having an annular slot with an inner diameter smaller thansaid center hole adapted to receive the edge of said center hole andthus providing inner clearance around said center hole when saidretainer threads are installed from the concave side of saidhemispherically shaped disc into said internal threads of said leadholder guide thus allowing angular rotation of the then joinedguide andretainer about the said hemispherically shaped guiding disc centerpoint.

2. A lead holder drafting compass in accordance with claim 1 in whichsaid boom extending over the drawing surface is provided with a crosssectional shape having symmetry about a vertical centerline and whoseupper width is greater than its lower width, said cross sectional shapealso presenting sur- 75 faces at the greater and smaller widths whoseconnection by a straight line projected downward will terminate on thedrawing surface at a point beyond a point of intersection of the saidvertical centerline of said cross sectional shape and the drawingsurface such that when outer surfaces of said lead holder guide cylindercontact surfaces of said cross sectional shape, the point of the guidedlead holder lead will fall upon said point of intersection of thevertical centerline of said cross sectional shape and the drawingsurface, or will fall beyond said point of intersection in the directiontowards the said straight line downward projection.

3. A lead holder drafting compass in accordance with claim 1 furtherincluding a gauge mark visibly inscribed upon the upper surface of saidrotating housing in a direction normal to the axis of said rods and alsoincluding a second gauge mark visibly inscribed upon the upper surfaceof said lead holder guide base in a direction parallel to first saidgauge mark, and with said gauge marks being a distance apartcorresponding to the distance between the vertical centerline of saidrotating housing vertical axis bearing hole and the vertical centerlinepassing through said hemispherically shaped disc center point.

4. A lead holder drafting compass in accordance with claim 1 in whichsaid transparent rotating housing suspended above the drawing surfacepossesses a lower flat and horizontal surface upon which are visiblyinscribed alignment marks coincidental with transverse centerlines ofsaid vertical axis bearing hole, such alignment marks being positionedat 90, at 45,

' and at other convenient distances apart, with one of said marks beingparallel to the axis of said rods.

5. A lead holder drafting compass in accordance with claim 1 in whichthe lower surface of said lead holder guide base possesses severalvisibly inscribed alignment marks, one of said marks being normal to theaxis of said rods and being discontinuous in the center portions of saidguide base while also projecting radially in either direction from avertical axis of said hemispherically shaped disc center point, andanother said mark being parallel to the axis of said rods and beingdiscontinuous in the center portions of said guide base while alsoprojecting radially in either direction from a vertical axis of saidhemispherically shaped disc center point.

1. A lead holder drafting compass comprising: a flat base with a bottomfriction surface, said base also including an upright handle memberhaving an extending boom projecting over a drawing surface, the end ofsaid boom containing in the vertical axis a screw attachment hole; atransparent rotating housing member, said housing having a vertical axisbearing hole with a counterbore on the bottom side through which ashoulder screw is inserted and installed into said vertical axis screwattachment hole, said housing being held suspended above the drawingsurface upon which said base rests by the head of said shoulder screw,said housing having two parallel horizontal clearance holes equaldistanced from said vertical axis bearing hole, said housing also havinga flat bottomed vertical hole lying between and partially intersectingat the diameter of said flat bottomed hole said parallel horizontalclearance holes; two rod members, longer than said housing, said rodsbeing parallel to each other and held within and passing through saidhorizontal clearance holes in said housing, said rods being joinedtogether at one end in one direction from said housing, and with theends of said rods protruding from said housing in the opposite directionbeing attached to a lead holder guide base; a cam lock member having ashort vertical portion with a recessed cam surface in and around saidcylindrical portion, and having a finger tab portion extendingvertically upward, and with said short cylindrical portion installedinto said flat bottomed vertical hole in said housing, and having saidrecessed cam surface contoured to cause alternately either looseness ora tightening of said rod members between said cam surface and outersurfaces of said horizontal clearance holes when said cam is rotated bysaid finger tab in a horizontal plane, and also having a portion of saidshort vertical cylindrical portion lying below said rod members andcaptured between said rod members and bottom of said flat bottomed hole;a transparent lead holder guide base member having a hemisphericallyshaped guiding disc portion concaved upward with a round hole in thecenter and with a hemispherical center point positioned at the drawingsurface, said hemispherically shaped disc being spaced off of thedrawing surface by two attached guiding pads equally spaced on oppositesides of said hemispherically shaped disc which contact the drawingsurface, and also positioned vertically by the joining of an attachedpad to the end of said rods which extend out of said rotating housingmember; a transparent lead holder guide membeR of hollow cylindricalshape having an upper guiding bore of diameter slightly larger than alead holder barrel, with the lower end of said lead holder guide havinga surface contacting the upper surface of said hemispherically shapeddisc and being concentric with and normal to said guiding bore, theinner lower end of said lead holder guide having an internal threadconcentric with said bore, there also being a small set screw hole witha set screw passing through the wall of said lead holder guide in thethreaded lower portion of said guide; a transparent lead holder guideretaining member, having external threads matching said internal threadsof said lead holder guide but also with an interfering diameter the sameas or smaller than said center hole of said hemispherically shaped disc,and having a lead hole of slightly larger diameter than a drafting lead,said lead hole also having a tapered entry at the upper end, with saidlead hole being concentric with said external threads, with said guideretainer also having a head at the lower end and being of largerdiameter than said center hole of said hemispherically shaped disc, saidhead being contoured to mate with the concave surface of thehemispherically shaped disc and also having an annular slot with aninner diameter smaller than said center hole adapted to receive the edgeof said center hole and thus providing inner clearance around saidcenter hole when said retainer threads are installed from the concaveside of said hemispherically shaped disc into said internal threads ofsaid lead holder guide thus allowing angular rotation of the then joinedguide and retainer about the said hemispherically shaped guiding disccenter point.
 2. A lead holder drafting compass in accordance with claim1 in which said boom extending over the drawing surface is provided witha cross sectional shape having symmetry about a vertical centerline andwhose upper width is greater than its lower width, said cross sectionalshape also presenting surfaces at the greater and smaller widths whoseconnection by a straight line projected downward will terminate on thedrawing surface at a point beyond a point of intersection of the saidvertical centerline of said cross sectional shape and the drawingsurface such that when outer surfaces of said lead holder guide cylindercontact surfaces of said cross sectional shape, the point of the guidedlead holder lead will fall upon said point of intersection of thevertical centerline of said cross sectional shape and the drawingsurface, or will fall beyond said point of intersection in the directiontowards the said straight line downward projection.
 3. A lead holderdrafting compass in accordance with claim 1 further including a gaugemark visibly inscribed upon the upper surface of said rotating housingin a direction normal to the axis of said rods and also including asecond gauge mark visibly inscribed upon the upper surface of said leadholder guide base in a direction parallel to first said gauge mark, andwith said gauge marks being a distance apart corresponding to thedistance between the vertical centerline of said rotating housingvertical axis bearing hole and the vertical centerline passing throughsaid hemispherically shaped disc center point.
 4. A lead holder draftingcompass in accordance with claim 1 in which said transparent rotatinghousing suspended above the drawing surface possesses a lower flat andhorizontal surface upon which are visibly inscribed alignment markscoincidental with transverse centerlines of said vertical axis bearinghole, such alignment marks being positioned at 90*, at 45*, and at otherconvenient distances apart, with one of said marks being parallel to theaxis of said rods.
 5. A lead holder drafting compass in accordance withclaim 1 in which the lower surface of said lead holder guide basepossesses several visibly inscribed alignment marks, one of said marksbeing normal to the axis of said rods and being discontinuous in thecenter portions of said guide base while also projecting radially ineither direction from a vertical axis of said hemispherically shapeddisc center point, and another said mark being parallel to the axis ofsaid rods and being discontinuous in the center portions of said guidebase while also projecting radially in either direction from a verticalaxis of said hemispherically shaped disc center point.